1. Field of the Invention
This invention relates generally to improvements in hammer bank assemblies useful in line printers. Such assemblies carry a plurality of hammers, each of which includes an impact tip carried on a flat coil and supported by a pair of flexible conductive members for substantially rotational movement about a horizontal axis perpendicular to the plane of the flat coil. A plurality of magnets are interleaved with the hammers so that the hammers are disposed in a permanent magnetic field. When a coil is energized, a force is developed on it to accelerate it from a rest position to impact against, paper, a ribbon and a font carrier band or a character drum mounted for rotation about an axis also extending perpendicular to the plane of the coil structure.
2. Description of the Prior Art
In order that the impact tips of all of the hammers in an assembly be presented on a common printline, it is necessary to accurately align and mount the hammer and magnet assemblies. In addition, it is essential that all of the hammers have a precise rest position with respect to the drum or font carrier band and that they be precisely fired and accelerated to impact when the drum or band is in the appropriate position. In addition, the accuracy of the mountings must be retained in spite of the great deal of vibration which occurs during the operation of the printer.
Various systems have been developed to accurately mount the hammers and magnets and to precisely establish the rest position of each hammer. In U.S. Pat. No. 3,643,595, issued to Helms, et al. on Feb. 22, 1972, an elongated mounting bar is provided defining a plurality of truncated V-shaped recesses along the length thereof. Each recess is shaped so as to receive and precisely position a foot member of a hammer module. Bolts are utilized to secure the hammer module to the mounting bar and to vertically position the hammer with respect to the mounting bar. Backstop screws having a deformable and resilient sleeve molded around them are utilized to adjust the rest position of the hammers.
U.S. Pat. No. 3,983,806, issued to Ishi on Oct. 5, 1976, discloses a mounting structure that includes at least one rigid cylindrical tube and a plurality of fastening members disposed therealong. Each hammer has a foot member which includes a recess of substantially semicircular cross-section dimensioned to conform to the periphery of the rigid tube. A plurality of magnets are mounted on a common foot member which has a recess of substantially semicircular cross-section also dimensioned to conform to the tube periphery. The semicircular surfaces serve to align the hammers and magnets with respect to the cylindrical tube. Multiple adjustable backstop screws are also utilized to establish the rest position of each hammer.
In U.S. Pat. No. 4,114,532, issued to Arzoumanian on Sept. 19, 1978, a magnet assembly for use in a hammer bank assembly is disclosed. The magnet assembly includes a plurality of spaced, relatively thin, substantially rectangular magnetic members mounted along first and second parallel rows. The magnetic members are aligned so as to define aligned gaps, each of the aligned gaps receiving a flat hammer coil. Various magnetic materials are employed for the magnet members.